1. Field of the Invention
The present invention relates to a sample feeding device for a trace detector and a trace detector with the sample feeding device.
2. Description of the Related Art
Currently commercially available detectors for safety inspection mainly detect harmful substances such as explosives and narcotics by ion mobility spectrometry. Such detectors comprise a sample feeding device. The sample feeding device can gasify and desorb solid particles or gas entering into the device. The gasified sample molecules are then introduced into an ionization region by air flow. After that, the ionized sample molecules enter into a drift region. The molecules are identified based on their drift time in the drift region. Most of commercially available detectors employ a semi-permeable membrane. The semi-permeable membrane can isolate an interior of a drift tube from the outside environment to prevent dust and foreign substance molecules from entering into the drift tube so as to ensure the cleanness of the interior of the drift. Only molecules (generally large molecules) having certain property can permeate the semi-permeable membrane to enter into the drift tube. The semi-permeable membrane exhibits a certain permeation ratio. A general permeation ratio is only around 10%. Therefore, most of the sample molecules are lost outside the semi-permeable membrane and few sample molecules enter into the drift tube, which results in considerable reduction in sensitivity of the detectors. In addition, the semi-permeable membrane generally operates at a high temperature, which requires a system to provide the semi-permeable membrane with an additional operation environment and heat. As a result, the operation power of the system is increased. If the detector is portable, power sustaining time of a battery will reduce. A detector without a semi-permeable membrane will produce a complex background peak since the drift region is in direct communication with the atmosphere environment and thus the interior environment in the detector tends to be polluted. In addition, a peak of a substance greatly varies and a position of the peak is unstable with the change of the exterior environment so that stability of detection operation is seriously degraded.